The present invention relates to a process for gasifying fine grained and dust-like solid fuel at an elevated pressure by passing the fuel by way of a pressurized lock basin into the gasifier.
One of the central problems of this type of gasification (partial oxidation) is the conveyance of the fuel into the gasifying chamber which is at a greatly elevated pressure.
To solve this problem a process has been proposed in which the fine grained or dust-like fuel is mixed with a suitable liquid, preferably water or low boiling hydrocarbons to form a suspension. The suspension is then condensed by means of a pump to the pressure level of the gasifier. The liquid is subsequently subjected to evaporation which causes a fluidization of the fuel particles which thus are gasified in a comparatively finely divided condition.
The shortcoming of this process lies in the fact that the evaporated liquid either takes part in the gasification and thus undesirably affects its results or that complex special installations are necessary to effect a prior separation and recirculation of the liquid.
Experiments have also been carried out (without publication) to convey the fuel from the supply tank which is under normal pressure into a space which is at elevated pressure by using a system of two lock basins which are alternatingly depressurized for filling and pressurized for evacuation. However, this approach proved to require expensive apparatus and substantial energy was necessary for the compression because of the alternating depressurization and condensing of an inert gas in the lock basins. This resulted in a substantial increase of the cost.
The assignee of the present case in its plant has also experimented with a system where the fine grained and dust-like fuel was directly advanced into the pressurized gasifier chamber by means of piston pumps, that is without using a mash with an auxiliary liquid. These tests were based on the assumption that an agglomeration of the moving fuel was not only unavoidable but desirable. The tests were therefore carried out in a manner that the fuel was condensed in a channel-like passage between the chambers of different pressure to form a sealing plug which was supposed to provide the sealing of the chamber at higher pressure against the space at atmospheric pressure. However, it was found that with this method the sealing plug did not provide an adequate gas and pressure seal. Besides, the grain size of the initial fuel could not be retained with this procedure. Instead, an agglomeration took place which resulted in briquette-like bodies.
In this process it was therefore necessary again to convert the formed sealing plug to a finely divided form because for the subsequent gasification it was absolutely necessary that the fuel was available in a loosened-up condition, that is, in fine grained or dust-like form. This re-comminution of the sealing plug constituted a substantial problem and this process was therefore not industrially used.
The present invention therefore has the object to provide for a process for gasification of fine grained and dust-like fuels at elevated pressure which avoids the difficulties described. It is in particular an object to provide for a process where the fuel is conveyed into the gasifying space in flowable and fluidizable form so that an intermediate re-comminuting of the fuel is not necessary.
It is also an object of the invention to provide for a process where the fuel can be conveyed in a comparatively simple manner from the supply tank which is at atmospheric pressure into the gasifying chamber which is at an elevated pressure without using for this purpose an auxiliary liquid.